ABSTRACT: The loss of large fishes from coral reefs can alter the composition of benthic assemblages and increase the abundance of smaller fishes at lower trophic levels. An experimental exclusion of medium and large fishes, maintained over 30 mo, had a major impact on the dynamics of 2 abundant damselfishes (Pomacentrusadelus and P.wardi) and altered their relative abundance in favour of the larger species, P.wardi. The territory size of both species inside exclusion cages increased by 20 to 50% in the first year, but then declined to their original size after a further 6 mo. The exclusion of larger fishes also led to an increase in the quantity and quality of food algae within damselfish territories. These results suggest that larger predatory and herbivorous fish influence the composition of coral reef communities not only directly, but also indirectly, by controlling the abundance and territorial activities of damselfish.